The preparation of substituted carboxylic acids and their anhydrides and esters from such unsaturated acids or acid derivatives as maleic anhydride, fumaric acid or itaconic acid has been known for some time. The products are useful in many ways. For example, they serve as anti-rust agents in lubricants and fuels and as intermediates in the preparation of metal salts, esters and nitrogen-containing products which are useful as viscosity index improvers, dispersants and the like in lubricants and fuels. Other uses are also known to those skilled in the art. For example, alkenyl succinic anhydrides are used in paper sizing, paper pulp processing, wet strength agents, epoxy curing agents, and plasticizer esters for polyvinyl chloride.
The methods heretofore used for the preparation of the substituted carboxylic acids comprise alkylation of the unsaturated acid or acid derivatives with an aliphatic hydrocarbon or halogenated aliphatic hydrocarbon at a temperature above above 200.degree. C. The earliest commercial processes generally utilized a thermal reaction wherein polyolefins of average molecular weight above about 200 were thermally reacted with maleic anhydride at temperatures in excess of 200.degree. C. However, this thermal reaction suffers from a relatively low degree of conversion and if an attempt is made to improve the degree of conversion by increasing the temperature or pressure, an undesirable degradation of maleic anhydride occurs with resulting formation of carbon dioxide, water and tarry solids (resin). For this reason, resort has been made to initial preparation of a halogenated hydrocarbon reactant followed by reaction of the halogenated hydrocarbon with maleic anhydride (chlorination processes).
However, in these chlorination processes, a relatively high concentration of chlorine is in contact with the reaction vessel for substantial lengths of time, necessitating the use of special equipment for the entire reaction and the final product frequently contains undesirable residual chlorine. In attempts to overcome the problems associated with both the thermal and chlorination processes, researchers have devised various multistage processes and processes utilizing combinations of the thermal process and chlorination process. See for example, U.S. Pat. Nos. 3,231,587; 3,912,764; and 4,110,349.